The overriding aim of this grant proposal is to translate technology developed with murine embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) to the clinical setting. More specifically, it is proposed to generate and characterize human inner ear sensory hair cell-like cells and supporting cell-like cells from ESCs and iPSCs. In Aim 1, human ESC-derived hair cell-like cells are being characterized immunocytochemically, morphologically, and functionally. In Aim 2, it is proposed to generate and characterize hair cell-like cells from human iPSCs, specifically from patients carrying mutations in the MYO15A gene. It is expected that the consequences of the mutant MYO15A gene are reflected in the cellular phenotype of hair cell-like cells generated from hearing loss patients. Further proposed is a rescue experiment with wild type MYO15A to restore the cellular phenotype in patient-derived hair cell-like cells. Finally, Aim 3 focuses on characterization of gap junctions in supporting cell-like cells derived from DFNB1 patients homozygous for the common GJB2 35delG mutation. It is proposed to compare cellular properties of 35delG homozygotes with severe-to-profound hearing loss to 35delG homozygotes with mild-to-moderate hearing loss. Measures include gap junction physiology and whole transcriptome analysis, which will be combined with genome wide association studies in a large cohort of DFNB1 patients. The goal of this endeavor is the identification of clinically relevant genetic modifiers, which is a first step toward developing strategies to ameliorate the typical severe phenotype associated with the 35delG/35delG genotype in DFNB1 patients.